Solid state power conversion devices that generate an AC or sinusoid type of output have special requirements with respect to uninterrupted or continuous power transmission. Gaps or interruptions in the output waveform cause severe radio frequency interference (RFI) or electromagnetic interference (EMI) which is difficult to suppress because any suppression network must also pass the desired AC waveform.
Conventional power control circuits use two output transistors, such that one transistor is on while the other is off. These transistors use a gate drive circuit that provides a positive voltage to the gate of one transistor while simultaneously supplying a negative voltage to the gate of the opposite transistor so that one transistor is on while the other is off. In order to insure that one transistor is completely off before the other is switched on, there is a delay between the negative transition of one gate drive signal and the positive transition of the other gate drive signal. This delay or "dead time" is designed so that variations in components, operating frequency and circuit noise will not defeat the dead time and cause both transistors to switch on simultaneously. The circuit could be seriously damaged if both transistors are turned on simultaneously because this would result in a very heavy current flow through the transistors and associated circuitry.
The dead time constitutes an interruption in the flow of power, and at high frequencies of operation, the dead time interval can constitute a significant percentage of each power pulse thereby limiting the total amount of power available at higher frequencies.
The present invention overcomes the problems with conventional gate drive circuits by minimizing the dead time while ensuring that there is no overlap in the on state of the power transistors. In addition it makes possible use of simple oscillators that do not incorporate sophisticated dead time circuitry.